class SF(object):
    instant = None

    def __new__(cls, *args, **kwargs):
        if cls.instant is None:
            cls.instant = super().__new__(cls)
        return cls.instant

    def __init__(self, password=''):
        self.password = password

    def get_content(self, content: bytes) -> bytes:  # 加密输入
        pass

    def put_content(self, pas_content: str) -> str: # 解密
        pass